Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Financial information for the Company's operating segments
Net interest income (loss)	$ 106,602	$ 113,147
Credit loss expense	26,350	1,500
Noninterest income	37,570	35,885
Noninterest expense	115,041	88,832
Income (loss) before income taxes	2,781	58,700
Income tax expense (benefit)	773	13,590
Net income (loss)	2,008	45,110
Total assets	13,900,550	12,862,395	$ 13,400,618
Goodwill	939,683	932,971	939,683
Community Banks
Financial information for the Company's operating segments
Goodwill	936,916		936,916
Insurance
Financial information for the Company's operating segments
Goodwill	2,767		$ 2,767
Operating segments | Community Banks
Financial information for the Company's operating segments
Net interest income (loss)	108,869	116,058
Credit loss expense	26,212	1,500
Noninterest income	30,683	29,585
Noninterest expense	109,284	83,313
Income (loss) before income taxes	4,056	60,830
Income tax expense (benefit)	1,280	14,286
Net income (loss)	2,776	46,544
Total assets	13,776,076	12,763,349
Goodwill	936,916	930,204
Operating segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	187	168
Credit loss expense	0	0
Noninterest income	2,940	2,879
Noninterest expense	1,886	1,815
Income (loss) before income taxes	1,241	1,232
Income tax expense (benefit)	330	320
Net income (loss)	911	912
Total assets	28,448	27,267
Goodwill	2,767	2,767
Operating segments | Wealth Management
Financial information for the Company's operating segments
Net interest income (loss)	441	350
Credit loss expense	138	0
Noninterest income	4,344	3,659
Noninterest expense	3,945	3,448
Income (loss) before income taxes	702	561
Income tax expense (benefit)	0	0
Net income (loss)	702	561
Total assets	71,895	58,971
Goodwill	0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(2,895)	(3,429)
Credit loss expense	0	0
Noninterest income	(397)	(238)
Noninterest expense	(74)	256
Income (loss) before income taxes	(3,218)	(3,923)
Income tax expense (benefit)	(837)	(1,016)
Net income (loss)	(2,381)	(2,907)
Total assets	24,131	12,808
Goodwill	$ 0	$ 0